Temperature compensation of a bias voltage of an amplifier is important because the amplifier is usually sensitive to changes in voltage of a power source. This is particularly important with the RF power amplifiers, such as LDMOS (Laterally Diffused Metal Oxide Semiconductor) devices, which are used for example in base stations of a radio system.
When a base station is located outdoors, the output voltage of a power source drifts with temperature, the variation of which can be very large causing a large variation in amplification. In prior art the temperature compensation has been performed, for example, by using a sensor and a microcontroller such that the microcontroller with a predetermined control algorithm controls the bias voltage provided by the temperature compensation circuit based on the temperature sensed by the sensor. This kind of solution is very complicated and expensive and requires a total circuit board area of tens of square centimetres.
The patent publication U.S. Pat No. 6,091,279 presents a simpler temperature compensation circuit which includes a temperature dependent component having a 2 mV/° C. temperature offsetting characteristic. With the temperature dependent component the circuit exhibits a constant slope of −2 mV/° C. as temperature changes. However, this solution has disadvantages. Since the slope is constant, the solution cannot be utilized if the need for compensation is different from the constant value.